Project project = new Project(dataDir + "Blank2010.mpp");

ExtendedAttributeDefinition resCostAttr = ExtendedAttributeDefinition.createLookupResourceDefinition(
        CustomFieldType.Cost, ExtendedAttributeResource.Cost5, "My lookup cost");

Value value1 = new Value();
value1.setNumericValue(BigDecimal.valueOf(1500));
value1.setDescription("Val 1");
value1.setId(1);
value1.setVal("1500");

resCostAttr.addLookupValue(value1);

Value value2 = new Value();
value1.setNumericValue(BigDecimal.valueOf(2500));
value1.setDescription("Val 2");
value1.setId(2);

resCostAttr.addLookupValue(value2);

project.getExtendedAttributes().add(resCostAttr);

ExtendedAttribute value = resCostAttr.createExtendedAttribute(value1);
value.setNumericValue(BigDecimal.valueOf(1500));
project.save(dataDir + "AddExtendedAttributesToRAWithLookUp_out.mpp", SaveFileFormat.MPP);